Oxidation, reduction and redox equations

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Question 2
Medium

The percentage by mass of iron in a steel nail is determined by a student.

The student:

  • reacts 500 mg500\text{ mg}500 mg of the steel nail with an excess of dilute sulfuric acid, so that all of the iron in the nail forms Fe2+(aq)\text{Fe}^{2+}(\text{aq})Fe2+(aq)
  • makes up the volume of the Fe2+(aq)\text{Fe}^{2+}(\text{aq})Fe2+(aq) solution to exactly 100 cm3100\text{ cm}^3100 cm3
  • takes 25.0 cm325.0\text{ cm}^325.0 cm3 portions of the Fe2+(aq)\text{Fe}^{2+}(\text{aq})Fe2+(aq) solution
  • titrates each portion with 0.0200 mol dm−30.0200\text{ mol dm}^{-3}0.0200 mol dm−3 potassium manganate(VII) solution.
1.

Write the equation for the reaction between iron metal and sulfuric acid.

[1]
2.

The titration results are shown in Table 1.

123
Final volume / cm3\text{cm}^3cm324.8048.4523.55
Initial volume / cm3\text{cm}^3cm30.0024.800.00
Titre / cm3\text{cm}^3cm324.8023.6523.55

Calculate the mean titre from the concordant results.

[2]
3.

Give the overall ionic equation for the oxidation of Fe2+\text{Fe}^{2+}Fe2+ by manganate(VII) ions, MnO4−\text{MnO}_4^-MnO4−​, in acidic conditions.

[1]
4.

State the colour change seen at the end point of the titration.

[1]
5.

Name the piece of laboratory apparatus used for:

  • measuring and transferring the 25.0 cm325.0\text{ cm}^325.0 cm3 portions
  • adding the potassium manganate(VII) solution
[2]
6.

The balance used to weigh the 500 mg500\text{ mg}500 mg of the steel nail has an uncertainty of ±0.005 g\pm 0.005\text{ g}±0.005 g for each reading. A weighing boat was weighed and its mass was subtracted from the total mass of the weighing boat and steel nail to determine the mass of the nail by difference. Calculate the percentage uncertainty in using the balance. Give your answer to two decimal places.

[2]

Oxidation, reduction and redox equations Questions

  1. A Level
  2. /Chemistry
  3. /Oxidation, reduction and redox equations